The recent demand for a magnetic recording apparatus with higher performance and lower price than before is actively promoting the development of new technologies to improve the areal recording density. The magnetic head along this line is required to have a narrower track width (for both read and write heads) and a smaller read gap than before. This is true also for the GMR (giant magnetoresistive) element as the read element, which needs a smaller size and a thinner film thickness. A GMR element consists basically of a free layer and a pinned layer (both of which are magnetic thin films) and a thin non-magnetic conductive layer held between them. It detects magnetic fields by utilizing the phenomenon that the conductive layer varies in resistance in response to the angle of magnetization of the two magnetic layers. Recently, the TMR (tunneling magnetoresistive) element has come into practical use, which has an insulating film in place of the non-magnetic conductive film and detects magnetic fields by utilizing the phenomenon that the tunnel current flowing across the two magnetic layers varies in response to the angle of magnetization in them.
The GMR element or the TMR element mentioned above has a magnetic layer called a pinned layer. This magnetic layer is pinned by the magnetic field arising from exchange coupling to an antiferromagnetic layer, so that its magnetization is not affected by external signal magnetic fields. The pinned magnetization generates magnetic charges to affect the movement of magnetization in the free layer. This problem is addressed by dividing the pinned layer into two magnetic layers, which are antiferromagnetically coupled to each other through a thin non-magnetic layer so that they have mutually antiparallel magnetization. This technology is disclosed in Japanese Patent Publication No. 7-169026 (“Patent Document 1”). It discloses that the magnetization of the pinned layer, which adversely affects the magnetization of the free layer, is cancelled, and this leads to improvement in the head characteristics. There has been disclosed in Japanese Patent Publication No. 9-16920 (“Patent Document 2”) a new technology to reduce to nearly zero the difference in magnetization between the two pinned layers which are anti-ferromagnetically coupled to each other. This technology helps increase the coupled magnetic field because the magnetic field due to coupling to the anti-ferromagnetic layer is inversely proportional to the magnetization of the pinned layer. Moreover, there is Japanese Patent Publication No. 2000-40209 (“Patent Document 3”) which discloses an idea of making the film thickness slightly different in view of the fact that the ferri-state does not easily occur when the film thickness is the same.
Japanese Patent Publication No. 10-302227 (“Patent Document 4”) discloses a technology of stabilizing the orientation of magnetization in the pinned layer by so adjusting the magnetostriction constant as to control the anisotropy of the pinned layer by means of the magnetoelastic effect. Japanese Patent Publication No. 2000-113418 (“Patent Documents 5”) and Japanese Patent Publication No. 2004-259914 (“Patent Document 6”) disclose a technology of stabilizing magnetization by making the magnetostriction constant positive in each layer for the automatic pinning structure (which is so designed as to fix magnetization only by the pinned layer without antiferromagnetic layer). Japanese Patent Publication No. 2005-310265 (“Patent Document 7”) discloses a dual spin valve head having two sets of stacked pinned layers in which each pinned layer has an adequate thickness and magnetostriction constant so that the pinned layer is magnetization free from flux reversal when the head slider is suffered mechanical damage through lapping process or contact with the recording medium. Japanese Patent Publication No. 2006-032522 (“Patent Document 8”) discloses an adequate composition of CoFe pinned layer to increase a coupling energy with IrMn layer for the head of so-called top spin value type in which an antiferromagnetic layer is stacked after the pinned layer stacking or the head of dual spin valve type in which two upper and lower pinned layers are stacked. Japanese Patent Publication No. 2006-018862 (“Patent Document 9”) discloses an adequate composition of the pinned layer for a large coupling energy between the pinned layer and the PtMn antiferromagnetic layer.
Moreover, the “Study on Pinned Layer of GMR Head for Its Magnetization Behavior and Its Improvement”, Japan Association of Applied Magnetism, K. Nishioka et al., Feb. 15, 2005; pp. 49-58 (“Non-Patent Document 1”) discloses a means for making the pinned layer resistant to electric discharges or mechanical shocks by allowing two pinned layers to have large anisotropic energies with a minimum of their difference.
None of the above-mentioned Patent Documents and Non-Patent Document disclose any concrete, comprehensive technologies for the magnetic head which produces a high output, with the pinned layer therein magnetizing without being affected by external disturbance, even when its magnetoresistive element is miniaturized to such an extent that both the track width and the height are smaller than 100 nm. In fact, the size of the magnetoresistive element is decreasing more and more (with the track width and the height becoming smaller than 100 nm) to meet requirement for improvement in recording density. The element with smaller dimensions has a decreased volume, and this results in a decreased energy accumulated for the pinning of magnetization of the pinned layer. On the other hand, the higher recording density leads to a decreased flying height and increased chances of the magnetic head coming into contact with the surface of the recording medium, with the latter causing the magnetization of the pinned layer to rotate. In addition, the magnetization of the pinned layer is subject to rotation by electric discharges and mechanical stress which are encountered during fabrication of the magnetic head.
One way to stabilize the magnetization of the pinned layer is to increase the accumulated energy for the magnetization of the pinned layer so as to reduce the effect of external disturbance. Moreover, the element should be so constructed as to be restored even though the magnetization of the pinned layer is changed by shocks.